Prior Art
As is well known in the art, strip has been cast between moving blocks, moving rolls, moving bands, and moving wheels or combinations of those. Strip has also been cast on to singular moving devices as in drag casting. In these processes the moving devices all function, at least partially, as molds to shape the casting. The moving component or components also function to transfer heat in order to solidify, at least partially, the cast strip. Examples of such casters are the well known block caster, twin roll caster and belt caster. Examples illustrative of practice may be found in Lenseus et al's U.S. Pat. No. 3,623,535; Wood et al's U.S. Pat. No. 4,934,441; Honeycutt et al's U.S. Pat. Nos. 4,934,443 and 4,940,077; Honeycutt's U.S. Pat. No. 4,945,974 and U.S. Pat. No. 4,979,557; Key's U.S. Pat. No. 5,251,686 and Ashok et al's U.S. Pat. No. 5,251,687 as well as in the extensive literature. Strips have also been cast from stationary, open ended molds as exemplified by Moritz's U.S. Pat. Nos. 3,451,465; 3,623,536 and 3,463,220.
Continuous casters are used extensively to produce castings of relatively pure alloys generally those of low strength such as alloys for foil and those of high electrical properties for windings or redraw rod. There has been little interest in producing strong, highly alloyed materials by continuous casting because relatively large investments were already in place for ingot metallurgy production and because traditions and art were already established for the production of strong alloys from ingots. However, such equipment eventually grows old. The real advantages, both technical and economic, that rapidly-solidified metallurgical-structures provide to strong "specialized" alloys have become increasingly accepted by academics and increasingly desired by industrial and government users alike.
Strip and like shapes can be cast with freezing rates in the accepted zone of "rapid solidification" i.e., solidification structures which are equivalent to or finer than the metallurgical structures achieved by air atomization of the alloy. There are well known and obvious economic and technical reasons why, given the same or equivalent metallurgical structural benefits, it is more desirable to produce a sheet, wire or foil product from cast strip rather than from atomized powder or from spray deposited strip.
Many entrenched, production people object to the concept of casting strong, specialized alloys in strip form, particularly, if the strip is for further fabrication to wrought product. Among the reasons for objecting is that even a small., "hard alloy" caster will produce too much metal for the current market of any hard alloy (not mentioning that it may idle entrenched, large furnace, ingot production facilities and large ingot breakdown mills). A rarely expressed reason for objecting is that the development of casters effective for the production of high quality, highly alloyed product may produce a second generation of "Mini Mills" and cause serious changes in the overall industry.
The concept of premium strength alloy sheet and other products being produced from rapidly solidified, continuously cast strip is slowly coming to the fore. Importantly for the practice of this invention, a caster really does not have to run at very high speed. Current, conventional, continuous caster thinking currently has it that casters should be run "wide open" at ever increasing speeds. In the instant teachings, the continuous caster should run at a speed satisfactory for making the best metallurgical structure and quality consistent with reasonable control leeway and safety. The unique production method and apparatus of this invention produces a rapidly solidified cast strip with minimal shrink porosity providing a strip which strip is especially suited for further fabrication.